Detection of Giardia trophozoites in archival pathology specimens of humansmall intestine

The examination of archival pathology specimens of human small intestine by light microscopy, field emission scanning electron microscopy (FESEM), and confocal scanning laser microscopy using fluorescent in situ hybridization (FISH) techniques was undertaken to better understand the epidemiology of Giardia. Giardia trophozoites were tentatively identified in the light micr oscope after hematoxylin and eosin (H&E) staining. The organisms were adher ent to the intestinal epithelium where they were also associated with stran ds of mucus within the lumen. Fluorochrome-conjugated antisense oligonucleo tide probes, developed for the 16S rRNA of Giardia lamblia and Giardia muri s, were used in FISH experiments with confocal scanning laser microscopy. P ositive identification of trophozoites could be obtained with the G. lambli a probe, but not with the G. muris probe. FESEM examination of serial secti ons adjacent to FISH-stained sections revealed trophozoites characterized b y their morphological features. The 16S rDNA probes specifically distinguis hed different species of Giardia, but whether multiple infections can occur within an individual host could not be determined.